GaAs-based semiconductor lasers are known and play a significant technological role. For instance, GaAs-based quantum well lasers emitting at about 0.98 .mu.m are inter alia used for pumping Er-doped optical fiber amplifiers in optical fiber communication systems.
In order to protect such lasers against deterioration and/or failure, the laser facets generally are coated with a layer (or layers) of insulator. This is particularly important in high power lasers such as the above referred-to 0.98 .mu.m pump lasers. If uncoated, such lasers frequently fall catastropically, due typically to a high surface state density caused by the presence of native oxides of GaAs-based materials.
A variety of facet coatings and facet coating techniques are known. See, for instance, M. Passlack et al., IEEE Journal of Selected Topics in Quantum Electronics, Vol. 1(2), p. 110, June 1995, which discloses Ga.sub.2 O.sub.3 facet coating. Other known coatings are SiO, SiO.sub.2, SiN.sub.x, ZrO.sub.2, and ZnSe. Vacuum cleaving and in situ deposition of Si on the laser facets has proven to provide effective passivation for 980 nm lasers. See, for instance, U.S. Pat. No. 5,063,173. However, this process is of limited manufacturing utility, due to its typically extremely low through-put, as a consequence of the need for cleaving in vacuum. Such vacuum cleaving typically results in loss of an appreciable portion (.about.half) of the processed wafer, and furthermore typically permits passivation of only a single laser bar at a time.
(NH.sub.4).sub.2 S wet chemical treatment of GaAs-based lasers has been found to reduce the surface recombination velocity by slight etching and formation of stable Ga-S and As-S bonds. See, for instance, U.S. Pat. No. 5,177,031, and G. Beister et al., Applied Physics Letters, Vol. 68(18), pp. 2467-2468 (April 1996). This method however typically provides only temporary passivation because the facets will re-oxidize, especially under high power operation. The wet chemical treatment is also difficult to control, and may result in deterioration of the optical quality of the facets, due to differences in the etch rates of the various layers.
In view of the importance of high power GaAs-based lasers for, e.g., optical fiber communications, it would be desirable to have available an effective and convenient facet passivation treatment suitable for use in a manufacturing process. This application discloses such a treatment.